JP7121153B2 - Aqueous ink composition for writing instrument and writing instrument using the same - Google Patents

Description

The present invention relates to a water-based ink composition for writing instruments. More specifically, the present invention relates to a water-based ink composition for writing instruments which is excellent in ink storage stability and handwriting color development. The present invention also relates to writing instruments using the composition.

BACKGROUND ART Conventionally, water-based ink compositions for writing instruments using white pigments such as titanium oxide have been known in order to obtain handwriting having concealability. Furthermore, it has become known that pastel or chromatic handwriting can be obtained while concealing the base by using a complementary color pigment or the like in combination with such an ink composition having high hiding properties. are being actively considered.

However, when a pigment having a high specific gravity such as titanium oxide is used, the pigment settles over time to form a so-called hard cake, which may make redispersion difficult. Therefore, attempts have been made to prevent the pigment from sedimentation by modifying various materials used in the composition or by using a dispersant in combination. However, although conventionally reported techniques can slow down the sedimentation velocity, hard cakes cannot be avoided over a long period of time, and the actual situation is that these measures have not led to sufficient results. is. Furthermore, measures such as increasing the viscosity of the ink by using a so-called gelling agent or a thickening agent, or developing a structural viscosity are being studied. However, when an ink composition in which these countermeasures are taken is used in a writing instrument using a pen tip such as a fiber core or a porous body, the amount of ink ejected may be reduced. Furthermore, when used in a writing instrument, the pigment settles at the tip of the pen, and the writing line may not be visible or the writing may be blurred. As described above, there is room for improvement in the conventional techniques with regard to the storage stability over time of ink compositions containing pigments with high specific gravity, and methods for further improvement are being investigated.

Japanese Patent Application Laid-Open No. 2003-138192 JP-A-11-217532 JP-A-2004-149681

The present invention makes it possible to create a dispersed state in which various components such as pigments do not settle over time and form a hard cake, and can be easily redispersed. To provide a writing ink composition which does not cause the pigment to sediment on the tip of a pen even when used for writing and which is excellent in the coloring of handwriting, and to provide a writing utensil using the same.

In the present invention, an aqueous ink composition for writing instruments (hereinafter sometimes referred to as "aqueous ink composition", "ink composition", or "composition") contains wet silica, hydrous kaolin, or the like. The above problems have been solved by, for example,
That is, the present invention
"1. An aqueous ink composition for writing instruments comprising pigment particles, wet silica, hydrous kaolin, an aggregation control agent, and water, wherein the aggregation control agent is a cellulose derivative. , the ink composition having an ink viscosity of 1 to 20 mPa·s at 20° C. and a rotation speed of 100 rpm (shear rate of 380 sec ⁻¹ ).
2. 3. The composition of paragraph 1, wherein the pigment particles comprise titanium oxide.
3. 3. The composition of paragraphs 1 or 2, further comprising a flocculating dispersant.
4. 4. The composition according to any one of items 1 to 3, wherein the hydrous kaolin has an average particle size of 0.1 μm to 5.0 μm.
5. A writing instrument containing the composition according to any one of items 1 to 4. "About.

According to the present invention, by blending wet silica into the water-based ink composition for writing instruments, it is possible to maintain the redispersibility of the ink composition and the stability over time compared to conventional writing instruments, while maintaining the pigment at the pen tip. It is possible to suppress the sedimentation of the ink, and to obtain a water-based ink composition for writing instruments which is excellent in writability and excellent color development of handwriting.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail. In the present specification, "parts", "%", "ratios" and the like that indicate compounding are based on mass unless otherwise specified.

A water-based ink composition for writing instruments according to the present invention comprises pigment particles, wet silica, hydrous kaolin, a cellulose derivative as an aggregation control agent, and water. It is 1 to 20 mPa·s under the condition of 100 rpm (shear rate 380 sec ⁻¹ ). Each component constituting the water-based ink composition according to the present invention will be described below.

(pigment particles)
In the present invention, pigment particles can be selected from any conventionally known ones. Pigments include inorganic pigments such as metal oxides or metal salts, as well as organic pigments such as organic dye pigments or lake pigments. In the present invention, inorganic pigment particles are preferred, and metal oxide particles are particularly preferred. In particular, since titanium oxide is white, it is preferable because various colors can be realized by combining with a complementary color pigment or the like described later. Furthermore, it is particularly preferable to use titanium oxide whose surface has been treated with alumina, since this improves the dispersion stability. As the pigment, a lustrous bright pigment such as an aluminum pigment can also be used.

The average particle size of the pigment particles is preferably 0.01 μm to 30 μm, more preferably 0.05 μm to 20 μm, even more preferably 0.1 μm to 10 μm. If the average particle diameter of the pigment particles is within the above numerical range, it is possible to suppress the sedimentation of the pigment particles at the pen tip such as the fiber core or porous body when combined with wet silica, resulting in good handwriting color development. is obtained. The average particle size of the pigment particles is, for example, a volume cumulative 50 particle size distribution measured by a laser diffraction method using a laser diffraction particle size distribution analyzer (trade name “Microtrac HRA9320-X100”, Nikkiso Co., Ltd.). % hour particle diameter (D50). As used herein, the term "average particle size" refers to the volume-based average particle size unless otherwise specified.

The content of the pigment particles in the aqueous ink composition is preferably 1 to 50% by mass, more preferably 10 to 40% by mass, based on the total mass of the aqueous ink composition. If the content of the pigment particles is within the above numerical range, it is possible to prevent deterioration of the ink jettability and maintain the concealability of the water-based ink composition and the handwriting formed using the same. .

(wet silica)
The aqueous ink composition according to the invention contains wet silica. The wet silica referred to in the present invention is amorphous silica synthesized by a wet method. They are secondary particles of 10 µm. In the present invention, wet silica has a higher specific surface area than dry silica and has many silanol groups on the surface, so that it interacts with pigment particles to form a loose crosslinked network. In addition, since loose and bulky aggregates can be formed with an aggregation control agent, an aggregation dispersant, etc., which will be described later, the inclusion of wet silica in the ink composition improves the dispersion stability of the pigment particles, Furthermore, the redispersibility of aggregates can be improved. On the other hand, when dry silica is used, the dispersion stability can be maintained, but the addition of a small amount causes structural viscosity and increases the viscosity of the ink, which is not preferable.

Furthermore, when using paper as a writing surface, wet silica exhibits a strong sealing effect, and can prevent pigment particles from entering between the fibers of the paper. , the effect of enhancing the coloring of handwriting is obtained.

The average particle size of wet silica is preferably 0.1 μm to 10 μm. If the average particle size of the wet silica is within the above numerical range, it can be stably dispersed in the ink composition, and a high effect of suppressing pigment sedimentation can be obtained. Further, from the viewpoint of obtaining higher color development properties, the thickness is more preferably 0.5 μm to 7 μm, further preferably 1 μm to 5 μm. The average particle size of the wet silica is, for example, measured by a laser diffraction method using a laser diffraction particle size distribution analyzer (trade name “Microtrac HRA9320-X100”, Nikkiso Co., Ltd.) when the volume of the particle size distribution is 50% cumulative. can be measured by the particle size (D50) of

Specifically, the wet silica that can be used in the present invention includes NIPSIL series (manufactured by Tosoh Corporation), Mizukasil series (manufactured by Mizusawa Chemical Industry Co., Ltd.), Carplex series (manufactured by DSL. Japan), Tokusil series (Oriental silica Corporation), Ultrasil series (manufactured by Evonik Degussa Japan), Zeosil series (manufactured by Rhodia), and Hisil series (manufactured by PPG).

The content of wet silica in the aqueous ink composition is preferably 0.1% by mass to 5% by mass, more preferably 1% by mass to 3% by mass, based on the total mass of the aqueous ink composition. preferable. If the wet silica content is within the above numerical range, it is possible to prevent the pigment from settling on the pen tip even when used in a writing instrument using a pen tip such as a fiber core or a porous body. Furthermore, the concealability of the water-based ink composition and the handwriting formed using it can be maintained.

(Agglutination control agent)
The water-based ink composition according to the present invention comprises a flocculation control agent. The aggregation control agent binds to relatively low-density aggregates formed by the wet silica described above, and further disperses hydrous kaolin, an extender, etc., which will be described later, in the water-based ink composition to increase bulkiness. It is capable of forming aggregates. This aggregation control agent prevents the water-based ink composition from becoming a hard cake and forms bulky aggregates, thereby improving redispersibility. As the aggregation control agent, for example, a cellulose derivative can be used, and two or more kinds of cellulose derivatives can be used in combination.

Cellulose derivatives include carboxymethylcellulose, methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, hydroxypropylethylcellulose and salts thereof. Among these, carboxymethyl cellulose is preferable because it can prevent hard cake formation of pigment particles and deterioration of redispersibility. This is because the carboxyl groups contained in carboxymethylcellulose easily adsorb to aggregates with relatively low densities, are uniformly present in the composition, and can inhibit aggregation between pigment particles, as described above. It is believed that this is because the filler, polyolefin resin particles, etc. can be dispersed, and the aggregate can be made bulky. Moreover, carboxymethyl cellulose is preferable because it has higher thermal stability than other cellulose derivatives, and its physical properties do not change even when the composition is heated.

The content of the aggregation control agent in the water-based ink composition is preferably 0.05 to 1.0% by mass, more preferably 0.1 to 0.5% by mass, based on the total mass of the water-based ink composition. is more preferable.

(hydrous kaolin)
The aqueous ink composition according to the present invention comprises hydrous kaolin. The hydrous kaolin referred to in the present invention is a flat or plate-like natural clay mineral mainly composed of aluminum silicate containing water of crystallization, which is obtained by refining kaolin clay, which is a natural clay mineral. In the present invention, as described above, the hydrous kaolin has a flat or plate-like particle shape. exhibits a strong filling effect, can prevent the pigment particles from entering between the fibers of the paper, and has the effect of further enhancing the color development of the handwriting.

In addition, the hydrous kaolin is uniformly dispersed in the relatively low-density aggregates formed by the pigment particles, the wet silica, and the aggregation control agent in the ink composition. Since high agglomerates are formed, redispersibility can be improved compared to the case of using calcined kaolin.

Furthermore, since the hydrous kaolin is placed in parallel with the paper surface when written due to its flat or plate-like particle shape when written, it does not scratch the paper surface even when overwritten. , it becomes possible to write without scraping the paper surface.

The average particle size of hydrous kaolin is preferably 0.1 μm to 5 μm. If the average particle size of the hydrous kaolin is within the above numerical range, the redispersibility of the ink composition and the color development of the handwriting can be enhanced, and scraping of the paper surface can be prevented. Further, from the viewpoint of obtaining higher color development properties, the thickness is more preferably 0.2 μm to 3 μm, further preferably 0.5 μm to 2 μm. The average particle size of hydrous kaolin is, for example, measured by a laser diffraction method using a laser diffraction particle size distribution analyzer (trade name “Microtrac HRA9320-X100”, Nikkiso Co., Ltd.) at a volume cumulative 50% of the particle size distribution. can be measured by the particle size (D50) of

Specific examples of hydrous kaolin that can be used in the present invention include ASP-G90 (average particle size: 0.2 μm), ASP-G92 (average particle size: 0.2 μm), ASP-072 (average particle size: 0.2 μm). 3 μm), ASP-101 (average particle size 0.4 μm), ASP-102 (average particle size 0.4 μm), ASP-170 (average particle size 0.4 μm), ASP-172 (average particle size 0.4 μm) , ASP-200 (average particle size 0.4 μm), ASP-400P (average particle size 3.5 μm), ASP-600 (average particle size 0.6 μm), ASP-602 (average particle size 0.6 μm), ASP -802 (average particle size 2.5 μm), ASP-900 (average particle size 1.5 μm), ASP-RO (average particle size 0.4 μm), ASP-NCX1 (average particle size 0.7 μm) (all products) Name, manufactured by BASF) Hydrite PXN-LCS (average particle size 0.68 μm), Hydrite RS (average particle size 0.77 μm), Hydrite Flat-DS (average particle size 5.0 μm), Barrisurf HX (average particle size 1 .49 μm), Eckalite 1 (average particle size 0.40 μm), Eckalite ED (average particle size 0.32 μm) (both trade names, manufactured by Imerys Specialties Japan Co., Ltd.), KaMin35 (average particle size 4.0 μm ), KaMin35B (average particle size 4.0 μm), KaMin80 (average particle size 0.5 μm), KaMin80B (average particle size 0.5 μm), KaMin90 (average particle size 0.4 μm), KaMin90B (average particle size 0.4 μm ) KaMinHG90 (average particle size 0.3 μm), KaMinTEK2001 (average particle size 0.25 μm), Polygloss 90 (average particle size 0.2 μm), Polyplate P (average particle size 0.8 μm), Polyplate P01 (average particle size 0.8 μm) , Polyplate HMT (average particle size 1.5 μm) (both trade names, manufactured by KaMin LLC), and the like.

The content of hydrous kaolin in the water-based ink composition is preferably 1% by mass to 20% by mass, more preferably 5% by mass to 15% by mass, based on the total mass of the water-based ink composition. If the content of the hydrous kaolin is within the above numerical range, it is possible to prevent the ink viscosity from becoming too high, hard cake formation, and scraping of the paper surface during writing. Furthermore, the concealability of the water-based ink composition and the handwriting formed using it can be maintained.

(resin)
The water-based ink composition can further contain a resin. Resins that can be used in the present invention include acrylic resins, urethane resins, ethylene-vinyl acetate copolymers, and the like. Water-soluble resins, resin emulsions in which resins are dispersed in water in the form of particles, and the like can be used. can be done. By including an acrylic resin in the water-based ink composition, the fixability of the water-based ink composition can be improved, and the abrasion resistance of the writing lines formed using the water-based ink composition can be further improved.

The acrylic resin used in the present invention is a polymer containing acrylic acid or methacrylic acid in repeating units. The acrylic resin may be dissolved in any alkali or dispersed in water.

As the acrylic resin, an acrylic acid ester resin, an acrylic styrene copolymer resin, an acrylic acid ester copolymer resin, a methacrylic acid ester resin, a methacrylic acid ester copolymer resin, or the like can be used. These resins are usually used as emulsions in many cases. Although the molecular weight of these acrylic resins is not particularly limited, those having a weight average molecular weight of 1,000 to 100,000 are generally used.

Specific examples of acrylic resins that can be used in the present invention include JONCRYL series (manufactured by BASF), Primal AC series (manufactured by Rohm and Haas Japan Co., Ltd.), JSRAE series (manufactured by JSR Corporation), Vinyl series (manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), Nikasol series (manufactured by Nippon Carbide Industry Co., Ltd.), Neocryl series (manufactured by DSM), Boncoat series (manufactured by DIC), and the like.

As the urethane resin that can be used in the present invention, polyether polyol copolymerization type, polyester polyol copolymerization type, and polycarbonate polyol copolymerization type urethane resin can be used.

Specific examples of urethane resins include Neorez series (manufactured by DSM), Hydran series (manufactured by DIC), Yuriano W series (manufactured by Arakawa Chemical Industries), Superflex (manufactured by Daiichi Kogyo Co., Ltd.), Merci series (manufactured by Toyo Polymer company) and the like.

Specific examples of the ethylene-vinyl acetate copolymer that can be used in the present invention include Aurysol series (manufactured by Showa Denko KK) and Sumikaflex series (manufactured by Sumitomo Chemical Co., Ltd.).

The content of the resin in the aqueous ink composition is preferably 0.5 to 15% by mass, more preferably 2 to 8% by mass, based on the total mass of the aqueous ink composition.

(aggregating dispersant)
The aqueous ink composition according to the present invention can contain a flocculating dispersant. Here, the aggregating dispersant is an agent that adheres to the surface of the pigment particles, keeps the distance between the pigment particles at a certain level or more while separating the pigment particles from each other, and can prevent the pigment particles from directly aggregating. be. As a result, aggregation of the pigment particles is suppressed, and even if aggregates are formed, aggregates with relatively low density are formed. Furthermore, since the pigment particles, the wet silica, the aggregation control agent, and the bulky pigment particles formed by the hydrous kaolin exhibit the above effects, the redispersibility can be further improved.

Alkylolammonium salts of polybasic acids are preferably used as such aggregation dispersants. A polybasic acid may have a plurality of acid groups, but examples thereof include acidic polymers having a larger number of acid groups, such as acrylic acid, methacrylic acid, polyvinylsulfonic acid, and polyphosphoric acid. In addition to this, polymers obtained by polymerizing unsaturated fatty acids such as crotonic acid are also examples of polybasic acids. Alkylolammonium salts of polybasic acids can be obtained by reacting these polybasic acids with alkylolammonium. Salts obtained by such reactions contain partial structures as shown below.
—C(=O)—N(—R ¹ )(—R ² —OH)
Here, R ¹ is an alkyl group and R ² is an alkylene group. The dispersing flocculant used in the present invention is preferably a polymer having such a partial structure. Such a polymer may have a plurality of the above structures, and its molecular weight is not particularly limited. is more preferable.

Also, depending on the pigment used, an acidic group such as a carboxyl group may exhibit a similar function. That is, polymers containing acidic groups can also be used as the aggregation dispersant.

In the present invention, the aggregating dispersant is bonded to the surface of the pigment particles by the groups as described above, and hydrogen bonds with other aggregating dispersant molecules, so that the main chain structure of the polymer enters between the pigment particles and the pigment particles It is considered to separate them.

Such flocculating dispersants are generally commercially available, for example Anti-Terra 203, Anti-Terra 204, Anti-Terra 206, Anti-Terra 250, Anti-Terra U, DISPER BYK-102, DISPER BYK-180, DISPER BYK-191 (both trade names, manufactured by BYK-Chemie), TEGO Disper630, TEGO Disper700 (both trade names, manufactured by Evonik Degussa Japan), and the like.

(Body material)
The water-based ink composition according to the present invention may contain an extender in addition to wet silica and hydrous kaolin within a range that does not affect its performance. In the present invention, the extender can be selected from any conventionally known ones. Specific examples include calcined kaolin, talc, mica, clay, bentonite, calcium carbonate, barium sulfate, and aluminum hydroxide. be done. Whiskers such as calcium carbonate, potassium titanate, magnesium sulfate, and calcium sulfate can also be used.

The content of the extender in the aqueous ink composition is preferably 1% by mass to 20% by mass, more preferably 5% by mass to 15% by mass, based on the total mass of the aqueous ink composition. If the content of the extender is within the above numerical range, it is possible to prevent excessive increase in ink viscosity, formation of a hard cake, and deterioration of ink jettability during writing. Furthermore, the concealability of the water-based ink composition and the handwriting formed using it can be maintained.

(complementary pigment)
The water-based ink composition according to the present invention may contain a complementary color pigment to adjust the color of the resulting writing line. In particular, when white titanium oxide is selected as the main pigment particles, various colors can be produced by combining with complementary color pigments. The complementary color pigment is not particularly limited, and pigments of various colors such as red, blue, yellow, green, white and black can be used. As complementary color pigments, for example, SP series (manufactured by Fuji Pigment Co., Ltd.) Emacol series, Sandye series (manufactured by Sanyo Pigment Co., Ltd.), Lumicol series (manufactured by Nihon Shokuryo Kagaku Co., Ltd.), EM Color series (Toyo Ink (manufactured by Shinroihi Co., Ltd.), Shinroihi Color Base Series (manufactured by Shinroihi Co., Ltd.), WA Color Series (manufactured by Dainichi Seika Co., Ltd.), and the like.

The content of the complementary color pigment in the aqueous ink composition is preferably 0.01 to 15% by mass, more preferably 0.1 to 10% by mass, based on the total mass of the aqueous ink composition.

(others)
In addition, the water-based ink composition may optionally contain surfactants, preservatives, wetting agents, antifoaming agents, rust inhibitors, pH adjusters, foam inhibitors, foam absorbers, shear thinning agents and viscosity enhancers. It may contain a regulator and the like.

(Aqueous ink composition for writing instruments)
The aqueous ink composition according to the invention preferably has a low viscosity. The viscosity of the composition can be measured using an E-type rotational viscometer (manufactured by Brookfield). Specifically, the viscosity of the water-based ink composition at 20° C. is preferably 1 to 20 mPa·s, preferably 8 to 18 mPa·s, when measured at a rotation speed of 100 rpm (shear rate of 380 sec ⁻¹ ). is more preferable. If the viscosity of the water-based ink composition is within the above numerical range, it is possible to improve the ink ejection property when used for writing instruments such as markers, and also improve the writing property on impermeable recording media such as films. do.

The pH of the aqueous ink composition is preferably 6.0 to 10.0, more preferably 7.0 to 9.0. If the pH of the water-based ink composition is within the above numerical range, the ink can be used without causing discoloration or an increase in ink viscosity. In the present invention, the pH value can be measured at 20° C. using, for example, an IM-40S type pH meter (manufactured by Toa DKK Co., Ltd.).

Although the reason why the water-based ink composition according to the present invention exhibits excellent redispersibility has not been clarified in detail, it is presumed to be due to the following mechanism.

As described above, the pigment particles, wet silica, and aggregation control agent form aggregates with a relatively low density, but especially when the pigment particles have a high specific gravity such as titanium oxide, the aggregates gradually become maximum over time. It is densely packed and becomes a hard cake. It is thought that by using hydrous kaolin together, the flattened, plate-like structure of hydrous kaolin will be present between aggregated pigment particles, which will inhibit close-packing and improve redispersibility. I get it. Furthermore, since the aggregating dispersant can be adsorbed on the surface of the pigment particles and maintain a constant distance between the pigment particles, it is believed that it works more effectively to inhibit close packing and further improves redispersibility.

The aqueous ink composition according to the present invention can be produced by any conventionally known method. Specifically, the necessary amount of each of the above components is blended and mixed with various stirrers such as a propeller stirrer, a homodisper, or a homomixer, and various dispersers such as a bead mill.

(writing implements)
The water-based ink composition of the present invention can be used in writing instruments such as marking pens and ballpoint pens with pen cores such as fiber tips, felt tips and plastic tips, ballpoint pen tips, and fountain pens with metal writing tips. can be done. Among them, when used in a writing instrument with a fiber tip or a felt tip, it can suppress the sedimentation of pigment particles in the tip, thereby improving the writing performance. Moreover, the porosity of the pen core is preferably 50 to 80%. When the porosity of the pen core is within the above numerical range, clogging of the pigment does not occur and an appropriate amount of ink ejection can be maintained.

The writing instrument of the present invention may be of a construction in which the water-based ink composition is directly filled, or may be provided with an ink reservoir or ink-absorbing body capable of being filled with the water-based ink composition.

The retracting mechanism of the writing instrument of the present invention is not particularly limited, and includes a cap type provided with a cap covering the pen tip, a knock type, a rotating type, a sliding type, and the like. Moreover, it may be of a retractable type in which the pen tip can be accommodated in the barrel.

In addition, the ink supply mechanism of the writing instrument is not particularly limited. For example, (1) a mechanism that includes an ink guide core made of a fiber bundle or the like as an ink flow rate control member and supplies a water-based ink composition to the pen tip; (2) A mechanism having a comb groove-shaped ink flow rate control member interposed therebetween to supply the water-based ink composition to the pen tip; and (4) a mechanism for directly supplying the water-based ink composition to the pen tip from an ink container or barrel provided with the pen tip.

In one embodiment, the writing instrument is a marking pen, and the pen tip is not particularly limited, and may be, for example, a fiber tip, felt tip, or plastic tip. It may be a brush pen type or the like.

In one embodiment, the writing instrument is a ballpoint pen, preferably a ballpoint pen with an ink backflow preventer.

The present invention will be explained using various examples as follows.
(Example 1)
An ink composition for writing utensils was obtained by stirring and mixing the following raw materials and blending amounts at room temperature for 1 hour. The viscosity of the obtained water-based ink composition was measured with an E-type rotational viscometer (DV-II+Pro, cone rotor CPE-42, manufactured by Brookfield). Specifically, the viscosity at 20° C. and shear rate of 380 sec ⁻¹ (rotational speed of 100 rpm) was 13 mPa·s.
・ Pigment particles 25% by mass
(Titanium oxide particles whose surface is treated with alumina, average particle size: 0.21 μm, manufactured by Tayca Corporation, trade name: JR-405)
・Wet silica 2% by mass
(Average particle size 2 μm, trade name: Mizkasil P-527, manufactured by Mizusawa Chemical Industry Co., Ltd.)
・Hydrated kaolin 10% by mass
(Average particle size 0.6 μm, trade name: ASP-600, manufactured by BASF)
・ Aggregate dispersant 1.5% by mass
(Alkylolammonium salt of high-molecular-weight acidic polymer, trade name: Anti-Terra 250, manufactured by BYK-Chemie)
・ Aggregation control agent 2% by mass
(Carboxymethylcellulose, 10% aqueous solution, trade name: F-907A, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)
・Acrylic resin 7% by mass
(Styrene-acrylic acid copolymer emulsion, solid content 47%, trade name: JONCRYL PDX-7600, manufactured by BASF)
・ Wetting agent 0.4% by mass
(Acetylene glycol, trade name: Dynol 604, manufactured by Nissin Chemical Industry Co., Ltd.)
・Preservative 0.2% by mass
(1,2-benzisothiazolin-3-one, trade name: Proxel XL-2, manufactured by Lonza Japan Co., Ltd.)
・Ion-exchanged water 61.9% by mass

(Examples 2-4, Comparative Examples 1-6)
Ink compositions of Examples 2 to 4 and Comparative Examples 1 to 6 were obtained by changing the types and amounts of components to be blended from Example 1 as shown in Table 1. Details of the materials used in these examples are as follows.
・ Titanium oxide (1) JR-405 (Al ₂ O ₃ treatment, average particle size: 0.21 μm, manufactured by Tayca Corporation)
・ Titanium oxide (2) JR-600E (Al ₂ O ₃ treatment, average particle size: 0.27 μm, manufactured by Tayca Corporation)
・ Wet silica (1) (Mizkasil P-527, manufactured by Mizusawa Chemical Industry Co., Ltd.)
・ Wet silica (2) (Mizkasil P-763, manufactured by Mizusawa Chemical Industry Co., Ltd.)
・ Dry silica (Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.)
・ Hydrous kaolin (1) (ASP-600, average particle size: 0.6 μm, manufactured by BASF)
・ Hydrous kaolin (2) (ASP-900, average particle size: 1.5 μm, manufactured by BASF)
・ Calcined kaolin (Satintone 5HB, average particle size: 0.8 μm, manufactured by BASF)
・Aggregating dispersant Anti-Terra 250 (alkylol ammonium salt of high-molecular-weight acidic polymer, manufactured by BYK-Chemie)
Aggregation control agent CMC (Carboxymethylcellulose trade name: F-907A, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)
・ Acrylic resin JONCRYL PDX-7600 (styrene-acrylic acid copolymer emulsion, solid content 47%, manufactured by BASF)
・ Urethane resin Neorez R-650 (polyether polyol copolymer urethane resin emulsion, solid content 38%, manufactured by DSM)

(Evaluation of redispersibility)
The water-based ink composition was placed in a sealed glass test tube with a diameter of 15 mm and allowed to stand at room temperature for 14 days. After that, each glass test tube that had settled once was shaken up and down, and the state of redispersion of the water-based ink composition was visually observed. Aggregation state was evaluated according to the following criteria.
A: Easily redispersed by shaking B: Redispersed by shaking, but it took a long time C: Not sufficiently redispersed by shaking D: Not redispersed by shaking

(Evaluation of handwriting color development)
For the pen tip, a bullet-shaped polyester fiber core tip with a porosity of 60% was used. With this marking pen, writing was performed on the writing test paper. At that time, handwriting color development was visually observed. Black paper (manufactured by Kishu Paper Co., Ltd., colored high-quality paper, medium thickness) was used as the paper for the writing test.
A: The handwriting covers the writing surface, and good handwriting is obtained.
B: Although the handwriting covers the writing surface, it is not sufficient, and the color of the writing surface is somewhat transparent.
C: The handwriting is visible, but the writing surface is hardly hidden, and the color of the writing surface is transmitted.
D: No handwriting was visible, and the writing surface was not covered at all.

(Evaluation of writing performance)
For the pen tip, a bullet-shaped polyester fiber core tip with a porosity of 60% was used. After writing on a writing test paper using this marking pen, the writing test paper was left for 30 days with the tip facing upward, and then the writing test paper was written on, and the state of the paper surface at that time was visually observed. Black paper was used as the writing test paper.
A: The handwriting covers the writing surface, and good handwriting is obtained.
B: Although the handwriting covers the writing surface, it is not sufficient, and the color of the writing surface is somewhat transparent.
C: No handwriting was visible, and the writing surface was not covered at all.

As is clear from the results in Table 1, the aqueous ink composition for writing instruments of the present invention was excellent in redispersibility of the ink and good in ink storage stability. Furthermore, when writing was performed with a marker using a bullet-shaped polyester fiber core tip with a porosity of 60%, the pen tip had good handwriting color development and good writing performance. Particularly in terms of writing performance, when the ink compositions of Examples were used, there was no sedimentation of the pigment in the tip, and good writing performance was obtained.

Claims (5)

An aqueous ink composition for writing instruments, comprising pigment particles, wet silica, hydrous kaolin, an aggregation control agent, and water, wherein the aggregation control agent is a cellulose derivative; A composition having a viscosity of 1 to 20 mPa·s at 20° C. and a rotation speed of 100 rpm (shear rate of 380 sec ⁻¹ ). 2. The composition of claim 1, wherein said pigment particles comprise titanium oxide. 3. The composition according to claim 1 or 2, further comprising a flocculating dispersant, said flocculating dispersant being an alkylol ammonium salt of a polybasic acid . The composition according to any one of claims 1 to 3, wherein the hydrous kaolin has an average particle size of 0.1 µm to 5.0 µm. A writing utensil containing the composition according to any one of claims 1 to 4.